Method of and apparatus for cleaning wood chips and the like



Jan. 10,1939. s R HMBERG 2,143,497

METHOD OF AND APPARATUS FOR CLEANING WOOD CHIPS AND THE LIKE Filed Nov.19, 19:54 2 Sheets-Sheet;

Jail. 10, 1939.

S. RAHMBERG METHOD OF AND APPARATUS FOR CLEANING WOOD CHIPS AND THE LIKEFiled Nov. 19, 1954 2 Sheets-Sheet 2 Patented Jan. 10, 1939 METHOD OFAND APPARATUS FOR CLEAN- OFFICE ING WOOD CHIPS AND THE Sven Bahmberg,Wallvik, Sweden; Axel Bostrom Martin and istrators of the deceasedApplication November 19 8Claims.

customarily prepared for treatment in digesters for the making ofsimilar materials.

I Thepresence of sawdust in digesters is highly objectionable, as isalso the presence of specks of dirt, bark,- or other impurities in pulpwhich is to be made into high grade papers. Hence, chips should bethoroughly cleaned before entering the digester. It is customaryjinpreparing wood for digesters, to out the wood by 'means of a chipperintochips which average about inch square. After the wood has been runthrough the chipp p r pulp, and for other per, the chips are often runthrough a crusher so as to break up over-size chips or splinters.According to common practice, the chips are run into a cylindricalscreen drum or shaking screens either directly from the chipper or fromthe crusher. The ordinary type of screen drum is rotated on an inclinedaxis, the upper portion of it being provided with holes about inch indiameter for the escape of sawdust and other undesirablematter; It isfound that holes of this size permit the escape of small chip fragmentsand splinters which are valuable as material for pulp, but which arelost with the sawdust. Furthermore, the ordinary screens now in use failto eflect a complete separation of dirt and sawdust from the chips,especially if the chips are moist or have adhering thereto bits of 1bark and the like which are rich in rosin. Par- 1 ticular trouble isoften experienced with the thin black bark surrounding the knotsin thewood, this bark breaking up into fine pieces in the chipper and tendingto adhere to the chips. Such fragments cause specks in the paperultimately made from the pulp, which are objectionable particularly inthe better grades of paper. 1 v

According to the present invention, the chips are subject to a treatmentwhich not only eflectively cleans the chips but also results in a savingof substantially all of the small chips and splinters which arecustomarily lost through the chip screens'now in common use. Accordingto the invention, the chips are tumbled in a rotating screen drumhavingopenings about $5; inch in diameter.

such as air, steam, or an equivalent, are projected from near theaxis-of the screen-toward the inner surface thereof.- These fluid jets,which are preferably of high velocity, impinge on the tumbling chips anddislodge therefrom all impurities, including dirt, sawdust, bits ofbark,

A numberof fineblast jets of fluid,

Bahmberg executors and adminestate of, said Sven Rahmberg,

1934, Serial No. 753,691 Sweden December 11, 1933 and the like. Suitablemeans is employed to promote and accelerate the flow of cleaning fluidthrough the meshes or holes of the screen so that all the looseparticles of sawdust or foreign matter are at once expelledfrom theinterior of the screen drum. If desired, apparatus may be provided forseparating the chips of proper size not only from sawdust and dirt butalso from large splinters of wood which may come from the chipper.

For a more complete understanding of the invention, reference may be hadto the following description of an embodiment thereof and to thedrawings, of which- Figure 1 is a longitudinal sectional view ofapparatus embodying the invention.

Figure 2 is a section on the 1ine 2-2 of Figure 1.

Figure 3 is a diagrammatic plan view of an installation of apparatusembodying the invention.

Figure 4 is a longitudinal sectional view of a screen drum forseparating large splinters from the chips in conjunction with thecleansing thereof.

Figure 5 is a section on ure 4. a

The invention may be embodied in a hollow screen drum Ill. The screenmay be of woven wire or of perforated sheet metal, the openings ineither event being preferably about y inchin diameter and as closelyspaced as is practicable. As shown, the screen drum may be in the formof an approximate cylinder, preferably increasing somewhat in diameterfrom the supply end to the discharge end; The screen drum i0 is mountedfor rotation on a suitable shaft II, this shaft being journaled inbearings l2 and I 3 carried by 'a frame ii. The portion of the shaft II,which extends through the bearing l2 and through the entire length ofthe screen drum in, is preferably hollow, the hollow portion terminatingin a reduced portion l8 which is journaled in the bearing l3. Projectingfrom the hollow shaft II at a suitably large number of points are blastnozzles 20. These nozzles may for the the line 5-5 of Figblast nozzlesadjacent to the ends of the screen drum I 0 are preferably inclinedtoward the 'middle of the screen as at 2| and 22. All of these blastnozzles communicate with the hollow interior of the shaft ll, so thatfluid supplied to the shaft ll under pressure is projected through thevarious nozzles toward the inner surface of the screen. The screen mayhave cylindrical extensions and 25 of sheet metal at its ends. On theinterior surface of the,screen Hi there may be any convenient number ofhelical fins or ribs 21 which extend to impart axial movement to thechips which are tumbling within the rotating screen drum. Thecylindrical extension 25, which, as indicated in Figure 1, is at thesupply end of the screen, may beprovided with similar fins 28. Chips tobe cleaned may be introduced into the extension 25 of the screen drum asby a chute which leads through a stationaryend plate 3|. At the oppositeor dis-, charge end of the screen drum is an end plate 32 having adischarge opening 33 therein. This opening may be of any convenientsize, shape and location, such, for example, as illustrated in Figure 2.

The screen is located within a casing which may be made approximatelyair-tight. This casing may be of suitable size and construction asdesired. As shown in Figure l, the casing is approximatelybarrel-shaped, having a pair of frusto-conical portions 35 and 36 whichare connected by a circumferential channel member 31. Thecircumferential channel in the member 31 communicates with an outlet orsuction vent through which the cleaning fluid which enters the screenthrough the nozzles 20, 2| and 22 may be sucked from the interior of thecasing. In the structure illustrated in Figure 1, the imperforateextensions 25 and 25 of the rotating screen drum project from the endsof the casing portions 35 and 38 and hence act as portions of thecasing, together with the end plates 3| and 32. Suf'flcient clearancesare preferably left between the stationary heads 3|, 32 and the movingparts 25, 26, and also between the stationary channel member 31 and theadjacent moving portions of the drum to ensure free rotation of thedrum. The casing is thus nearly air-tight except for the supply chute30, the discharge opening 83, the nozzles 20, 2| and 22, and the suctionvent 40 so that a strong suction can bemaintained through the meshes orholes of the screen ill. As indicated in Figure 3, the screen drum illmay be rotated by means of a suitable power-transmission device such asa gear wheel which is mounted on the reduced end portion l6 of the shaftii and which meshes with a pinion 5| mounted on the shaft of a motor 52.Air or other cleaning fluid may be supplied to the hollow shaft H bymeans of a connecting pipe leading from a suitable air pump 56 driven bya motor 51. The suction vent 40 may be suitably connected to a pump Bilwhich may be driven by a motor 6|. Any other desired driving means maybe employed for rotating the screen and for operating either or both ofthe pumps.

In operating the mechanism, the screen drum may be rotated at anysuitable speed, depending on its diameter, the speed of rotation of a23-foot screen drum being preferably from 10 to 15 R. P. M. Wood chipsto through the chute 30 directly from the chipper, or from a conveyor,or from any other suitable source. The chips enter the end compartmentadjacent to the smaller, end of the screen drum and are moved alongaxially by the helical flns 28 as the screen drum is revolved. Theseflns also assist'in tumbling the chips thoroughly within the screen asthey progress from the supp y end thereof to the discharge end. Duringtheir progress through the screen drum, tumbling chips are subiected toblasts-of cleaning fluid, such'as cleaning operation.

be cleaned are supplied air, which is pumped into the hollow shaft IIand is discharged through the nozzles 20, 2| and 22, preferably at highpressure. These nozzles are preferably of comparatively small diameterso that, although the cleaning fluid is projected at high velocity intothe interior of the screen, the total volume of fluid thus entering thescreen is not excessive. The flow of cleaning fluid outwardly throughthe perforations of the screen is expedited by suction maintained on thevent 40 as by a suction pump 50. As indicated on the drawings, the crosssectional area of the vent 40 is large in comparison with that of theindividual nozzles 2|! so that the air or other fluid discharged at highvelocity but in relatively small volume through the nozzles 25 isreadily carried off by the vent 40. This pump is preferably of suchcapacity as to be capable .of maintaining the pressure in the spacebetween the screen i0 and the casing members 35 and 36 somewhat belowatmospheric pressure, if desired, so that there may be a slight inflowof air through the chip supply and discharge openings in the casing. Theskin friction of the rotating screen causes a rotary flow of the airwithin the casing in the direction of rotation of the screen. itself,this air also tending to flow toward the channel 31 and thence outthrough the vent 40, carrying with it the sawdust and dirt particleswhich have been dislodged from the chips by the blasts of air or othercleaning fluid from the nozzles. The inclination of the nozzles 2| and22 toward the middle of the screen tends to drive the dirt-laden airwithin the screen drum toward the middle of the screen to pass throughthe screen opposite the channel 31 and 3 the suction vent 40, and alsotends to prevent flow of air toward the chip supply and dischargeopenings in the ends of the casing. The chips, after progressing fromthe supply end of the screen to the discharge end, fall through thedischarge opening 33 and are caught by a receptacle or conveyor (notshown).

In the chipping process as ordinarily practiced, the pulp-wood logs arefed to the chipper at an angle so that the knives of the chipper strikeobliquely across the quently happens that a log which is nearly all cutwill turn so that the chipper blades cut it lengthwise, this resultingin large slivers which are undesirable for the digester. According tothe present invention, such large slivers can be separated from thechips simultaneously with the To this end, I may provide apparatus suchas is illustrated in Figures 4 and 5. This embodiment of the inventionmay include a revoluble drum 10, similar to the drum 35, withan-extension 1| at the supply end rotating against an end plate 12 andhaving oblique ribs 13 to feed the chips received through the chute 30.A suction channel 11 surrounds the grain of the wood. Itfremid-periphery of the drum 10 where the halves m of the drum areseparated, this channel leading to suction outlet 18 which preferablyleads to a suitable pump as illustrated in Figure 3. If desired,suitable flexible strips 19 may be carried by the channel 11 to bearagainst the adjacent portions of the rotating drum 10 so as'to close theclearance between these parts.

Within the drum 10 and rotatable therewith, are a pair of coaxialscreens and 8|, the outer screen 8|! having relatively small openingstherein, the inner screen 8| having larger openings. For example, thescreen 80 may have openings varying from V5 inch at the supply end toabout inch at the opposite end thereof. The inner screen may haveopenings varying from about inch at the supply end to 1 or 2 inches atthe a other end. These aperture sizes and those here inaft-er given areby way of example only and not by way of limitation. The screens 80 andill preferably diverge somewhat in diameter toward the discharge end.Beyond the discharge end of the drum H1 is an imperforate extension 83which may be substantially a continuation of the screen member fill. Theextension t3 revolves with the drum 1t and terminates in an opendischarge 7"1. The inner screen 3! extends through the interior of theextension 33 and projects a substantial distance beyond the dischargeend thereof, this portion of the screen 85 having large perforations ormeshes of the order of 1 or 2 inches. To promote axial movement by thechips in the drum, helical ribs 35 may be mounted on the inner surfaceof the screen dd and drum extension dt as indicated.

Chipped wood is received by this apparatus direct from the chipper andis at once subjected to the cleaning action of high-velocity jets offluid such as air, steam or an equivalent. lihe particles of sawdust anddirt dislodged by the jets are immediately sucked through the meshes ofthe screen and are discharged through the outlet 18. The chips andslivers of proper size pass through the meshes or perforations of thescreen iii as they travel toward the discharge end. The oversizefragments remain within the screen 8! until discharged through its openend beyond a partition wall conventionally indicated at 81. The cleanedchips of proper size are discharged from the end of theextension 83 onthe rear side of the near side of the partition wall it? and are thenready for delivery to a digest-er.

It is evident that various modifications and changes may be made in theembodiment of the invention herein shown and described without departingfrom the spirit or scope thereof as defined in the following claims.

Iclaim:

1. A method of cleaning wood chips and the like, which comprisestumbling the chips in a rotating hollow screen drum, projecting fluidjets radially from near the axis of the drum toward the inner surfacethereof, and projecting fluid jets from near the axis at points adjacentto the ends of the screen obliquely toward the middle of the drum.

2. A method of cleaning wood chips andthe like, which comprisestumblingthe chips in a rotating hollow screen drum, projecting fluid jets fromnear the axis of the screen drum toward the inner surface thereof,including jets adjacent to the ends of the screen and inclined towardthe middle thereof, and maintaining a lower than atmospheric pressure atthe outer surface of the screen.

3. Amethod of cleaning wood chips and the like, which comprisescontinuously feeding chips into one end of a hollow screen drum, continuously rotating the drum, permitting chips to escape from the oppositeend of the drum, and

projecting fluid jets from near the axis of the drum toward the innersurface thereof, including jets adjacent to the ends of the screeninclined,

nozzles being adjacent to the ends of the screen and being inclinedtoward the middle thereof.

5. Apparatus for cleaning wood chips or the like, comprising anelongated approximately cylindrical screen rotatable on a horizontalaxis, said screen having openings therethrough of sufficient size forthe passage of standard chips, means for introducing chipped wood intoone end of said screen, an outer screen coaxially surrounding a portionof the first said screen and.

extending for a portion of the length thereof from the supply end, saidouter screen having relatively small openings, means for projecting jetsof fluid radially from near the axis of said outer screen, and means formaintaining suction at the outer surface of said outer screen.

6. A method of cleaning wood chips, which comprises tumbling the chipsin a rotating screen drum, subjecting the tumbling chips to a series ofjets of gaseous fiuld at sufiiciently high velocity to dislodge from thechips particles of matter adherent thereto, and maintaining a lower thanatmospheric pressure surrounding the sides of the drum, wherebydischarge of said gaseous fluid through the ends of the drum is avoided.

7. Apparatus for cleaning wood chips, comprising a rotatable screen drumhaving openings in the sides thereof approximately ,4; inch in diameter,a casing enclosing said drum and having apertures'for the admission ofchips into one end of the drum and the discharge of chips from the otherend of the drum, means within the drum for projecting a series of fluidjets toward the inner surface of the screen, and means for maintainingin said casing a lower than atmospheric pressure, whereby discharge offluid from said jets through said apertures is avoided.

, 8. Apparatus for cleaning wood chips or the like, which comprises abarrel-shaped casing having end-openings for supply and discharge ofchips and a suction vent midway between the ends, a frusto-conicalhollow screen drum tapering in diameter from the discharge and of thedrum to the supply end and rotatable on its aids, helical fins securedto the inner face of the screen to rotate therewith whereby to assistthe chips in their advance toward the discharge end-opening, and meansfor projecting jets of fluid radially from near said axis toward theinner surface of the screen.

